The present invention relates to hydraulic systems for work vehicles, and more particularly to work vehicles having appendages such as boom assemblies with bucket portions or other movable elements.
Various work vehicles such as construction work vehicles (e.g., loader-backhoes) include movable appendages such as boom assemblies that can be used to scoop up or otherwise move material such as soil, sand and gravel. Such boom assemblies often include multiple segments that are movable relative to one another, and the boom assemblies in particular typically include buckets or other movable elements at the far ends of the boom assemblies away from the vehicles. These end elements of the boom assemblies are typically the portions of the boom assemblies that come into direct contact with the material to be scooped up or moved.
In various circumstances, the material that is being scooped up or otherwise moved by the boom assembly of a work vehicle has a gummy or otherwise adherent consistency. Such materials can include various forms of clay, for example. In particular, the consistency of the material is such that, as the end element of the boom assembly encounters the material, a portion of the material tends to adhere to the end element. Further because of the material""s consistency, the material does not tend to fall off or otherwise become dislodged from the portion of the boom assembly to which it is adhering. Consequently, some of the material can become attached to the boom assembly during a digging cycle or job and remain attached during the digging cycle/job, such that not all of the material in the boom assembly is dumped out after each digging cycle/job.
Continued adhering of the material to the end element can be undesirable for a variety of reasons. First, the adhering of material to the end element can reduce the volume within the end element and consequently reduce the amount of material that can be picked up and moved by the end element in a given amount of time. Also, because the material is attached to the end element, the work vehicle can appear to be unsightly and uncleanly. Further, in certain circumstances, it can be unsuitable to use the bucket or other end element of the work vehicle to move other materials as long as the first material is still adhering to the end element. Thus, it can become necessary to remove the adhering materials from the end element by way of a separate operation after usage of the work vehicle.
Another problem encountered by work vehicles with boom assemblies is that the end elements can have difficulty in initially plowing or otherwise moving through the material that is to be scooped up or otherwise moved. This is particularly true in the case of hard materials such as black-top or frozen or frosted dirt. It also is the case where the material has either a gummy or adherent consistency, or where the material has been compacted under pressure such that it is difficult to pierce.
It is possible to operate conventional construction work vehicles in such a manner as to address these problems. In a conventional construction work vehicle, the position of the bucket or other end element is typically controlled by one or more hydraulic cylinders that each have head and rod chambers. The provision of hydraulic fluid from a pump toward a cylinder, as well as the allowing of hydraulic fluid to exit the cylinder toward a tank, are in turn determined by a valve. An operator can rapidly switch the position of the valve so that, at certain times, hydraulic fluid pressure from the pump is directed toward the head chamber while hydraulic fluid is allowed to exit the rod chamber toward the tank and, at alternating times, hydraulic fluid pressure from the pump is directed toward the rod chamber while hydraulic fluid is allowed to exit the head chamber toward the tank.
By alternating the status of the valve and consequently the hydraulic fluid pressure exerted at the cylinder, the bucket or other end element experiences a changing force that can result in a vibrational movement of the end element. This vibrational movement can dislodge materials that are adhering to the end element. Also, the vibrational movement can facilitate plowing or other movement of the bucket or other end element through material that is difficult to pierce through, since the vibrational movement tends to cause the material to break apart.
Despite the effectiveness of this conventional operation for creating vibration of the bucket or other end element, this operation has certain disadvantages. First, to obtain this vibration in conventional construction work vehicles, the operator must repeatedly switch the position of the valve. More specifically, the operation typically requires repeated switching of the position or statuses of one or more valves associated with the hydraulic cylinder(s) so that, at certain times, the valve(s) couple the pump to the head chamber of the cylinder(s) and the tank to the rod chamber of the cylinder(s), and at alternating times, the valve(s) couple the pump to the rod chamber of the cylinder(s) and the tank to the head chamber of the cylinder(s). This manual switching operation can become arduous since, for example, it can require repeated moving of a lever on the part of the operator (in the case where spool valves are employed).
Second, in certain circumstances, the bucket or other end element will undesirably tend to have an overall movement in a particular direction as it is being vibrated, rather than maintain its original or nominal position. This can occur because the operator is unable to consistently vary the pressures applied back and forth to the bucket so that the bucket maintains its original position. That is, the operator in some situations will tend to apply pressure in one direction too long during vibration of the bucket, which can tend to move the bucket away from its original position.
This problem can be exacerbated when the bucket or other end element is carrying a load or is otherwise experiencing a force from an outside source, which can include a force provided by the material through which the end element is attempting to plow or move. In such circumstances, it can be difficult for the operator to vary the position of the valve in a way that counteracts the influence of these forces such that the original, nominal bucket position is maintained. Consequently, as the positions of the valve(s) are repeatedly switched, the end element may move downward under the force of gravity, move away from the material through which the end element is attempting to move, or otherwise move away from its original position.
Such movement of the bucket or other end element can be a problem in a number of situations. For example, when the bucket is being operated in close proximity to other machinery, such as a dump truck, it can be a nuisance for the operator to have to repeatedly align the bucket to its original position when vibration of the bucket moves the bucket away from that original position. Also, movement of the bucket or other end element away from the material through which the end element is attempting to move can be counterproductive in that it reduces the ability of the end element to cut through the material.
Additionally, while movement of the bucket or other end element away from its original position is undesirable in many circumstances, there are also circumstances in which it is desired that the element experience an overall movement in a particular direction as it is vibrating. For example, this can be the case when the bucket is being used to loosen or break through hard materials along the ground, such as black-top. In these circumstances, it can again be difficult for an operator to manually perform the vibration operation in the desired manner. However, in this case, the difficulty arises because it is difficult for the operator to manually vary the position of the valve in a manner whereby the resulting amount of movement of the bucket in one direction consistently exceeds the amount of movement in the other.
A third disadvantage associated with the conventional ways of creating vibration of the bucket or other end element is that, while the rapid switching of the valves does produce some vibration, it is difficult to obtain large amounts of vibration, even when the hydraulic fluid pressure provided by the pump is quite large. Because the hydraulic fluid pressure is typically provided from the pump to the hydraulic cylinder by long rubber pump lines that run the length of the boom assembly and are not completely rigid, there is a significant amount of hydraulic capacitance that exists between the pump and the hydraulic cylinder. This hydraulic capacitance limits the vibrational effects that occur at the hydraulic cylinder as a result of the switching on and off of the hydraulic pressure from the pump (and the switching off and on of the coupling of the hydraulic cylinder to the tank).
Because of these disadvantages associated with the conventional manner of creating vibration at the buckets or other end elements of boom assemblies of construction work vehicles, it would therefore be desirable if a new system was developed for implementation on a construction work vehicle (or other work vehicle) that made it possible to create vibration at the bucket or other end element of the vehicle""s boom assembly (or to create vibration at another appendage of the work vehicle.) It would be particularly advantageous if the new system could be operated to easily remove material that is adhering to the end element of the boom assembly. It would additionally be desirable if such a system also could be employed to enable the end portion of the boom assembly to more easily plow or otherwise move through material of an adherent or compacted nature.
It would further be desirable if such a system could be cost-effectively implemented on existing designs of construction work vehicles (or other work vehicles). It would also be desirable if such a system could be operated without significant manual control or exertion on the part of the operator of the construction work vehicle. It would additionally be advantageous if the system could operate to control the vibration of the end element so that, depending upon the circumstance, the vibration either would not move the end element away from its original, nominal position or, alternatively, the vibration would move the overall position of the end element in a particular desired direction. It would additionally be advantageous if the system""s ability to provide vibration was not significantly limited by capacitance in the hydraulic lines coupling the pump and tank with the hydraulic cylinder.
The present inventors have discovered that it is possible to cause vibration to occur in a bucket or other end element of a boom assembly of a construction work vehicle by repeatedly switching the positions/statuses of only one pair of valves that control the flow of hydraulic fluid to and from only one of the two chambers of the hydraulic cylinder (or cylinders) employed to control the positioning of the end element. While the statuses of the first pair of valves are switched, each of the second pair of valves that control the providing of hydraulic fluid to the other of the two chambers of the hydraulic cylinder is maintained in a closed position such that hydraulic fluid cannot be provided to that cylinder chamber from or to the pump or the tank.
By selecting the load-bearing chamber as the chamber with respect to which hydraulic fluid flow is restricted, the end element can be prevented from experiencing any substantial movement due to the force of gravity or other outside forces, including the force of the material through which the end element is attempting to move. Although the flow of hydraulic fluid to the other chamber is switched by the first pair of valves, that chamber does not provide force to the end element for counteracting the outside forces being experienced by the end element, and consequently the switching of the valves has only the relatively minor vibrational impact upon the positioning of the end element. Additionally, the present inventors have discovered that the switching of the first pair of valves can be controlled automatically in response to a single command provided from the operator, and thus requires little manual effort or control.
In another embodiment of the invention, the inventors have discovered that it is possible to cause vibration to occur in a bucket or other end element and at the same time impart motion of the element in a particular direction in a consistent manner. The combined vibration and overall motion is produced by repeatedly switching the positions/statuses of the two pairs of valves that control the flow of hydraulic fluid to and from the two chambers of the hydraulic cylinder (or cylinders). The statuses of the valves are varied in a complementary manner so that, when the first pair of valves are switched so that one cylinder chamber is coupled to the tank, the other pair of valves are switched so that the other cylinder chamber is coupled to the pump. By repeatedly alternating the statuses of the valves, vibration is produced. Further, by switching the valves so that one of the chambers of the cylinder tends to be coupled to the pump for a greater amount of time than the other chamber of the cylinder, overall motion of the end element in a particular direction can be produced.
In particular, the present invention relates to an apparatus for creating vibration of an appendage of a work vehicle. The apparatus includes a hydraulic cylinder coupled between a first portion of the work vehicle and the appendage and including a first chamber, a second chamber, and a piston, where movement of the piston results in corresponding movement of the appendage with respect to the first portion of the work vehicle. The apparatus further includes a valve assembly coupled between the first and second chambers, a pump, and a tank, wherein the valve assembly governs whether hydraulic fluid is provided from the pump to the first and second chambers and to the tank from the first and second chambers. The apparatus additionally includes a control element coupled to the valve assembly, where the control element in response to a command causes a status of at least a first portion of the valve assembly to repeatedly alternate with time so that the hydraulic fluid is alternately provided from the pump to the first chamber and provided to the tank from the first chamber, so that vibration occurs at the piston and is in turn provided to the appendage.
The present invention further relates to an apparatus in a work vehicle. The apparatus includes an appendage coupled to a portion of the work vehicle. The apparatus further includes a hydraulic cylinder coupled between the portion of the work vehicle and the appendage and including a load-bearing chamber, a non-load-bearing chamber, and a piston, where movement of the piston results in related movement of the appendage with respect to the portion of the work vehicle. The apparatus additionally includes a flow regulation means for determining whether hydraulic fluid is provided from a hydraulic pressure source to the non-load-bearing chamber, and from the non-load-bearing chamber to a fluid reservoir. The apparatus further includes a control means for controlling the flow regulation means, where the control means is capable of automatically operating in at least one of a first mode in which the appendage is caused to vibrate without significantly moving from an original position, and a second mode in which the appendage is caused to vibrate and also to experience an overall movement in a particular direction.
The present invention additionally relates to a method of creating vibration at an appendage of a work vehicle. The method includes (a) coupling a hydraulic cylinder between a first portion of the work vehicle and the appendage, and (b) coupling a valve assembly between a pump and first and second chambers of the hydraulic cylinder, and between a tank and the first and second chambers. The method additionally includes (c) receiving a command to provide vibration of the appendage, and (d) controlling a first portion of the valve assembly so that hydraulic fluid flows from the pump to the first chamber and a second portion of the valve assembly so that hydraulic fluid at least one of flows from the second chamber to the tank and is prevented from flowing to and from the second chamber. The method further includes (e) controlling the first portion of the valve assembly so that hydraulic fluid flows from the first chamber to the tank and the second portion of the valve assembly so that hydraulic fluid at least one of flows from the pump to the second chamber and continues to be prevented from flowing to and from the second chamber. The method additionally includes (f) repeating (d) and (e) over a period of time so that the vibration is created at the piston and at the appendage.